The present invention relates to optical focusing control systems for optical recording systems. In particular, the present invention relates to a focusing intialization or loading system to be activated when an opticl recording system is first turned on or must be reactivated when it is in an out of focus condition for some reason. The present invention may use as an input the analog signals derived from known focusing systems which are designed to operate an objective lens focusing system in an optical recording system when a near focus condition has already been achieved. However, such systems which operate from a given near focus condition cannot achieve that near focus condition from a condition in which the objective lens is far from a focused condition. Thus, an object of the present invention is to provide a system to drive the objective focusing lens in an optical recording system to a sufficiently near focus condition that a near focus control system can take over driving the objective lens element.
Known to Applicant is U.S. Pat. No. 3,974,327 which relates to a focusing system for an optical data recording device. The system described in the patent relates to a system in which the objective lens is initially moved from a position furthrest away from the recording media towards the media and towards a focused position. When a near focus condition is detected, the patent is directed towards developing a control system to protect the objective lens from crashing into the media by immediately driving it away from the media while leaving it in a near focused condition. This patent does not anticipate the logic of the present invention which detects a near focus condition and activates a near focused automatic control system while maintaining a protective watch on the focusing function.
A near focus control system is shown in U.S. Pat. No. 4,123,652. That patent describes a system in which four focusing elements are arranged in a square or quadrature system to detect a focusing light spot and to produce four separate output signals. The detectors may be diode light detectors of a known type. The system employed in that patent is an astigmatic focusing system. The patent shows that the output signals of the various detectors may be combined in a particular fashion to produce a signal suitable for controlling a focusing system in a near focused condition. Of course, the same system using the detectors will continuously produce an output signal as long as light is detected on the detecting area.
The system as described in that patent is characterized in that the system will produce a zero level output signal when in a far out of focus condition either too far from the recording media or to too close to the recording media as well as at an exact focused condition. In a near to focus condition, the outputs of the detectors are combined in such a fashion as to produce a bipolar signal when the objective lens is in a near to focused condition on either side of the focus condition. The Figs. in the referenced patent as well as the text of the patent describes the shape of the light impinging on the detector area in these near to focus conditions as well as the output signal combinations to be used with the detectors in order to produce an output signal as described.
Other focusing systems may exist and may be developed with which the present focus initialization system may be used. Such systems may be used with a quadrature detector in which the focusing system produces the same type of output signal as described herein in which a bipolar signal has peaks at near to focus conditions. A two detector system may be used in astigmatic or other focusing systems to produce a bipolar output signal. Other systems may exist in which such an output signal may be generated using other types of detector patterns. The present invention is not limited as to the focusing system or as to the detection system used. The present invention will work with any focusing system which may be configured to provide the appropriate variable output signal having a bipolar relationship to the near to focus and focused conditions.